Unlike primary batteries, which cannot be recharged, rechargeable batteries can be repeatedly charged and discharged. Low capacity rechargeable batteries that use single battery cells may be used as power sources for various portable electronic devices such as cellular phones, notebook computers, and camcorders. High capacity rechargeable batteries that use tens of battery cells connected to each other in a battery pack may be used as power sources for driving motors such as in hybrid electric vehicles (HEV). Rechargeable batteries may be classified according to their external shape into cylinders, prisms, or pouches.
Rechargeable batteries generally include an electrode assembly which is formed by spirally winding positive and negative electrodes and a separator into a jelly-roll configuration. The separator is positioned between the positive and negative electrodes and serves as an insulator. The electrode assembly may alternatively be formed by stacking a positive electrode, a negative electrode, and a separator. The electrode assembly is housed in a case, which is closed with a cap assembly having an external terminal.
The structure of an electrode assembly of a prismatic rechargeable battery is described in Japanese Unexamined Patent Application Publication Nos. 2000-40501, and 2001-38475, the entire contents of which are incorporated herein by reference.
Compared to a cylindrical rechargeable battery, a prismatic rechargeable battery is likely to have unnecessary internal “dead space” between the case and an electrode assembly housed therein due to its structure.
The dead space results from the intrinsic shape of the electrode assembly. In the case of electrode assemblies that have a jelly-roll configuration, the electrode assembly has edges that are partially rounded. The rounded edges create gaps within the case, resulting in dead space when the electrode assembly is positioned in the internal space of a battery can.
The dead space may cause an excessive amount of electrolyte to be introduced during fabrication of a rechargeable battery due to the volume of the gap, resulting in wasted electrolyte and performance deterioration of the rechargeable battery.
Particularly, it is necessary for motor driving rechargeable batteries in hybrid electric automobiles to have a configuration adapted to achieve high power, and such problems may be more serious in the case of a large-sized battery than a small-sized battery.